Die,and method of manufacturing calibrated rivets

ABSTRACT

A GUN-SHAPED DIE FOR MANUFACTURING RIVETS MADE OF AN ELASTIC ETAL HAVING AT ONE END A SLIGHTLY INWARDLY TAPER ING FLANGE MEMBER AND AT THE OTHER END A FLANGE MEMBER APPROXIMATELY TWICE AS GREAT OR GREATER IN DIAMETER THAN THE INWARDLY TAPERING FLANGE MEMBER. THE PORTION OF THE GUN-SHAPED DIE BOUNDED BETWEEN THE TWO FLANGE MEMBERS HAS A THICKNESS SUFFICIENT TO WITHSTAND ELASTIC DEFORMATIONS AND GENERALLY THE THICKNESS OF THIS PORTION WILL BE APPROXIMATELY EQUAL TO THE BORE OF THE DIE.

E. AURIOL March 16, 1971 DIE, AND METHOD OF MANUFACTURING CALIBRATED RIVETS Filed May 25, 1967 fl/l/twzve 220 flue/04 flrr Mai-Ks M United States Patent Office 3,570,031 Patented Mar. 16, 1971 3,570,031 DIE, AND METHOD OF MANUFACTURING CALIBRATED RIVETS Eloi Auriol, Flourens, Haute-Garonne, France, assignor to Ateliers de la Haute-Garonne ets Auriol & Cie Filed May 25, 1967, Ser. No. 641,327 Claims priority, application France, May 27, 1966,

Int. or. 13211; 1/58 US. 'CI. -24 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a die for manufacturing parts, such as rivets, that are perfectly calibrated; it further relates to a method of using such a die with a conventional punching machine, said method being applicable to the manufacture of rivets or the like made of binding metals.

It is well known that the dies used heretofore for manufacturing rivets by cold or hot forming do not make it possible to obtain rivets with uniform, perfectly calibrated shanks, and that serious difficulties often arise in connection with the economical manufacture of rivets made of binding metals. For in the manufacture of such parts, bar sections have one of their ends inserted into a die and are then struck axially on the other end with a rivet set of a shape suited to the type of head to be obtained. An ejection device is inserted into the die and acts as an abutment for the bar section and as the means for ejecting the finished rivet. Now the clearance required to enable a section to be inserted into the die allows a certain amount of swelling of the rivet shank to take place under the effect of the forming operation, which can in turn cause a slight expansion of the die. With a single-mould, guntype die, this phenomenon will result in friction during the ejection process that can produce a grabbing effect on the shank, and this can be particularly serious with binding metals such as titanium alloys. In the case of multiplemould dies of the kind described in French Pat. No. 598,343, this swelling effect will usually cause ovalization of the rivet shankregardless of the accuracy with which the moulds are machineddue to the natural tendency of the moulds to open in response to the punching forces and the formation of burrs matching the mould joint lines.

With the aim of avoiding this swelling it has been proposed to apply transverse forces to the die in order to offset the punching reactions, but it has been found that the resulting, clamping will not avoid the formation of burrs matching the mould joint lines, nor permit frictionless ejection from a conventional gun-type die.

The present invention aims at overcoming these disadvantages, and one of its objects is accordingly to provide a die for manufacturing parts and in particular rivets that have a uniform and perfectly calibrated shank.

It is another object of the invention to provide a die permitting economical production rates, in the case notably of rivets made of unusually binding metals.

A die accordingto the present invention is capable of use with a punching machine designed to perform the conventional forming operations on a bar section referred to precedingly, the machine being devised to apply transverse clamping forces to the die for offsetting the transverse reactions to the axial punching forces.

The subject die of this invention takes the form of a gun made of a springy metal and its outer wall is provided with means for presetting the clamping load distribution, said wall being thick enough to withstand the axial punching loads yet thin enough to permit a contraction in response to the clamping that ensures intimate contact of its internal surface with the side of the bar section.

Obviously, the diameter of the die bore must be related to the diameter of the bar section so as to leave sufficient clearance for insertion of the section in addition to the ejection clearance required for an economical output of rivets, having regard for the elastic radial deformations of the die resulting from the heterogeneous clamping. Further, a die according to the invention produces perfectly calibrated shanks free of burr marks.

The invention likewise relates to a method of centripetally loading a die of the kind hereinbefore described by means of a punching machine designed to perform the conventional operations of restraining the die and forming the bar section.

The method according to this invention further consists in distributing, in predetermined fashion, the die restraining loads and in applying the same,

at the earliest, after the reaction of abutment of the section against the ejector, and, at the latest, upon initiation of the forming operation,

and in then releasing said forces,

at the earliest, upon completion of the forming operation, and at the latest, at the start of ejection of the formed element.

This method ensures a prestressing of the die appropriate to the forming-reaction distribution that results in a reduction in the diameter of the die bore suflicient to limit swelling of the bar section whilst ensuring a correct ejection clearance by removing the restraining forces after the forming operation.

In this way, the subject method of the present inventon permits economical production rates of, for example, rivets made of binding metals.

Further particularities and features of the invention will become apparent from the description which follows with reference to the accompanying non-limitative exemplary drawings, in which:

FIG. 1 shows in longitudinal section a conventional forming clamp gripping a die according to the invention.

FIG. 2 shows in perspective the clamp equipped with the die of FIG. 1.

FIGS. 3 to 6 schematically illustrate the steps involved in a rivet-manufacturing process.

FIG. 7 schematically illustrates in cross-section a dieholding vice of a punching machine.

FIG. 8 shows in longitudinal section an alternative embodiment of the die shown in FIG. 1.

Reference to FIG. 1 shows a die shaped as a gun 8 the bore 9 of which is shaped at one end into a frustoconical recess 10 that is extended by a cylindrical chamber 11.

The top and bottom of the gun are formed respectively with flanges 12 and 31 which bound between them a portion of smaller annular section than the flange sections.

This particular die is intended for forming short rivets involving only small restraining forces. Flange 12 tapers slightly, with the diameter in the plane A being greater by a few hundredths (two-hundredths, say) of a millimeter than the diameter at the plane B. This difference ensures, at the end plane A, a maximum stressing in order to compensate for the effects of the force generated when forming the rivet head.

Gun 8 is carried within the through passage of a clamp 1, of any convenient known type, which clamp consists of a bushing formed with two sets of longitudinally extending radial slits 14a, 14b, debouching or emerging at each end of the bushing.

Gun 8 is made of spring steel and can be fitted with its clamp and engaged between a fixed jaw and two movable jaws 16a, 16b, associated to the rams 17a, 17b of a vice (see FIG. 7). These various members enable radial clamping forces to be exerted against the clamp in the direction of arrows f4.

Alternatively, recourse may be had to the die shown in FIG. 8. This die takes the form of a gun 8a formed at one end with a reaction flange 31a, while the die portion included between the two transverse planes A and B tapers somewhat so that the diameter in plane A is greater by a few hundredths of a millimeter than the diameter in plane B This dimensional difference is designed to provide, in end plane A a maximum stress effect identical to that referred to precedingly.

The die portion included between plane B and the base of flange 31a is cylindrical and its diameter is equal to the smaller diameter of the tapering portion, whereby the clamp 1a has a rigorously cylindrical bore.

A conventional punching machine equipped with such members then allows the following operations to be carried out in succession:

Feeding out of a bar 6 (whose section is equal to that of the gun bore 9 minus the insertion clearance) a section 5 having the required rivet dimensions (FIG. 3).

Conveying section 5 opposite die 8.

Inserting, with the aid of a cup-shaped die-set 4, the section 5 into the die 8 until it abuts against a punch 3 (see FIG. 4, arrow f3).

Operating the rams 17 to tighten the clamp against the gun.

Obtaining, by the effect of die-set 4 (FIG. 5, arrow F), a rivet head 7a on the free end of said section remote from the end bearing against punch 3.

Moving away die-set 4, releasing the clamp and using the punch 3 to eject the rivet by its shank 7!) (FIG. 6, arrow f1).

As soon as the punch reverts to its initial position, the machine is ready to perform an operating cycle identical to the one just described.

It is possible at this juncture to explain how such a die will enable uniform output of calibrated rivets to be maintained.

Because the rams 17 tend to squeeze together the sectors between the slits 14 and clamp 1, transverse forces are transmitted to the flanges 12 and 31, thereby producing a clamping effect on the gun 8.

This in turn produces elastic deformations resulting in a slight reduction in diameter of bore 9 which is effective in clamping the section 5 therein.

During the very brief interval when the striking force F is applied, the rivet head 7a is formed by the action of the cup-shaped rivet-set while the rivet shank 7b firmly gripped in the bore 9 and bearing against punch 3 undergoes a slight dilation limited by the radial dimensions of prestressed bore 9.

As a result, the distortions permitted by the clearance provided for insertion of the feed bar into a gun-die are for all practical purposes eliminated; further, after the centripetal restraining forces cease to be exerted by the films he die opens by natural resilience and reverts to its initial bore diameter, thereby providing a clearance which, though somewhat less than the insertion clearance, is nonetheless suflicient to ensure correct ejection.

The insertion and ejection clearances will obviously depend on the dimensions and the nature of the sections to be formed, and the figures which follow are thought to be useful for situating their comparative magnitudes.

For rivets commonly known as 4 mm. rivets, the following dimensions will be found suitable:

Inner diameter of die 4 Diameter of bar section -e 3.98 Whence, bar insertion clearance Rivet shank diameter 3.99 Whence, ejection clearance For manufacturing rivets from metals sensitive to ejection friction, however, the ejection clearance must be raised to 1.5/100 mm. or mm.

During the forming process of the section 5, the punch 3 and the die 8 clamping it jointly form, with cup-shaped die-set 4, a system which is the seat of complex stress distributions and transfers; due however to the difference in the diameter of flanges 12 and 31, the stresses set up by the clamping forces exerted by the rams are made proportional to the reactions caused by the forming force F. Indeed, because of this difference in diameter, the unit clamping stresses are greater on flange 12 (in the region where the blank experiences greatest distortion in forming the head 71:) than the flange 31 which serves as on thrust point for the other end of clamp 1.

For the same reasons (FIG. 8), the portion of die 8a extending between plane A and flange 31a is the seat of clamping stresses greater than those engendered in this flange.

Thus, in the case of a 4 mm. rivet, the force F is substantially equal to 1 metric ton, whereas the radial ram forces are jointly equal to 25 metric tons, so that a diameter is chosen for flange 31 equal to roughly twice the diameter of flange 12 in order that the clamping stresses at the top of the die should be twice as great as those at the bottom.

Further, the waisted shape of the outer lateral wall of gun 8, between the two flanges 12 and 31, results in a thickness roughly equal to the diameter of the bore 9 in order to accommodate the aforesaid elastic deformations, the metal from which the gun is made being naturally chosen to provide the required degree of elasticity.

Thus, use may be made of conventional steels containing 1.8% of carbon and 13% of chromium, or 0.45% of carbon and 1.5% of silicon, the latter grade of steel additionally including traces of chromium and molybdenum. It is possible to make a die according to this invention with a metal of this type without any special difficulty, using routine machining operations and hardening operations appropriate to the nature of the metal.

From the foregoing description it will be readily, understood that prior art expansion devices such as that described in US. Pat. No. 3,202,432, which utilizes a relatively thin tubular sleeve designed to cooperate with radial sectors for generating clamping forces responsively to a hydraulic pressure, would not make it possible, if transposed to the forming art, to produce calibrated rivets at an economical production rate because such devices do not include means for distributing the clamping forces according to the way in which the reactions set up by the forming loads are distributed. Moreover, the sleeve referred to embodies, in its middle portion, helicoid slits which provide a central zone of deformation conducive to the formation of burrs on the shank of the forged part that would inevitably hinder ejection of the part.

It goes without saying that, without departing from the scope of the invention, other means could be used for distributing and proportioning the die clamping forces to the stresses due to the punching reactions: by way of example, the gun could be substantially tubular and adapted to be gripped by rings of sizes appropriate to the forces to be applied, such rings being provided in the areas of intensive reaction, and the thickness of the gun wall being in all cases sufiicient to withstand the punching forces.

Moreover, systems utilizing multiple rams or the like could be used to apply different clamping forces over determinate areas of a die.

Clearly, many changes and substitutions of parts may be made in the specific form of embodiment described hereinabove without departing from the spirit and scope of the invention.

What I claim is:

1. In a forging device for forming a rivet from a calibrated cylindrical blank and including a cup-shaped tool, a clamp, a die mountable in the clamp and provided with an aXial bore therethrough adapted for receiving the blank with a portion thereof protruding out of the die from a head end of the die toward the tool, punch means operatively connected with the die for punching the blank against the tool to form a rivet with a shank in the die and a formed head protruding out the head end thereof, and means for removing the formed rivet from the die; an improvement comprising in combination:

the clamp having at least three arcuate sectors,

the die comprising a single piece of elastically deformable material with its bore in an unstressed state having a diameter sufficiently greater than that of the blank to permit insertion of the blank therein, jaws operatively connected to the clamp to compress the arcuate sectors of the clamp radially against the die through the period when the punch means are operational to offset radial forces generated during formation of the rivet head so that on release of the jaws the die returns substantially to its diameter in its unstressed state to facilitate removal of the shank from the die,

the die having a shank end remote from its head end with an intermediate portion therebetween,

the die tapered outward from the intermediate portion to the head end for achieving maximum stressing by the jaws on the head end to compensate for the forces generated in forming the rivet head,

the die further provided with an outward projecting flange at its shank end which is adapted to anchor the shank end in the clamp.

2. The combination according to claim 1 with the die having a constant outside diameter between the intermediate portion and the flange at the shank end and substantially equal to the smallest diameter of the tapered portion between the intermediate portion and the head end.

3. The combination according to claim 2 with the clamp provided with slits between the arcuate sectors and arranged axially along the outer circumference of the die.

References Cited UNITED STATES PATENTS 1,261,084 4/1918 Wilcox 10-24 1,597,927 8/1926 Simons 10-24 1,929,184 10/1933 Clouse 10-24 1,961,442 6/1934 Johnson 10-24 2,028,652 1/1936 Mulatier 10-24 3,202,432 8/1965 Cameron 279-4 2,227,810 1/ 1941 Mitchell 10-24 2,278,293 3/1942 Watson 10-24 CHARLES W. LANHAM, Primary Examiner E. M. COMBS, Assistant Examiner 

